Master-slave computer systems have been utilized extensively in various corporate, government and academic environments, particularly in applications requiring advanced computing power. With a master-slave computer system, a relatively powerful host computer such as a mainframe computer, a midrange computer, or server computer, handles the majority of the computer operations, with a number of non-programmable, or "dumb", terminals interfaced with the host computer to do little more than receive input from users and output the results of operations performed by the host computer.
In a master-slave computer system, terminals are typically coupled to a host computer through a master-slave communication link, with the host computer acting as the master and the terminals acting as slaves. The host computer controls the flow of all information across the master-slave communication link, and all communications with any terminal typically pass through the host computer. One such master-slave communication link, for example, is the Twinax attachment interface from International Business Machines Corporation, which defines one cabling and low-level master-slave protocol suitable for use with host computers and the like. A transmission protocol such as the Twinax Data Link Control (TDLC) protocol developed by International Business Machines Corporation is often used on such interfaces to communicate data thereon. Moreover, typically the data is further encapsulated in a higher-level network architecture such as Systems Network Architecture (SNA), also developed by International Business Machines Corporation, for use in the master-slave environment.
While master-slave computer systems are still in widespread use, personal computers have to some extent supplanted such computer systems in a number of environments. Personal computers continue to increase in performance, and thus, are capable of handling many tasks that once required a powerful host computer--and often at a significantly lower cost.
In some environments, personal computers may be installed in addition to or in lieu of the non-programmable terminals in a master-slave computer system, typically using suitable master-slave interface hardware (e.g., an interface adapter card) and a terminal emulation computer program that in effect enables a personal computer to mimic a non-programmable terminal when communicating with a host computer. This permits, for example, the personal computers to be used for local operations, as well as for host-based operations such as creating and accessing shared folders on the host, transferring files with the host, initiating computer programs on the host, etc.
More typically, however, personal computers are coupled to one another and/or to a server computer over a local area network (LAN) and/or wide area network (WAN) interface, which permits individual computers coupled to the LAN and/or WAN to communicate directly with one another without the necessity of sending information through a host computer (as is required with a master-slave communication link). Data communicated in this manner is often referred to as "internetworking data", and an internetworking protocol is typically used to define the manner in which such data is transmitted over a LAN and/or WAN. Most internetworking protocols rely on network addresses to identify computers and other devices connected to a network. Using network addresses, operations such as "peer-to-peer" operations, where any computer coupled to a network can pass information to any other computer coupled to the network, and "broadcast" operations, where a single transmission may be routed to multiple computers in a group, may be supported.
One popular protocol for transmitting information in this manner is the Transmission Control Protocol/internet Protocol (TCP/IP), which permits computers in a network to be assigned unique network addresses commonly referred to as "IP addresses". Many of the most popular user applications rely heavily on TCP/IP communication. For example, much of the Internet is configured for TCP/IP-based communication, and thus, a number of popular applications such as web browsers, email clients, groupware applications, file transfer protocol (FTP) clients, etc., support the TCP/IP protocol. Many operating systems implement TCP/IP-compatible networking that provides a standard set of TCP/IP-based functions that may be used by an application executing on such systems so that the specific operations associated with handling TCP/IP communications are transparent to the applications.
Due to the fundamental differences between master-slave communication links and peer-to-peer enabled internetworking network interfaces, however, it may be difficult to support internetworking communication with personal computers coupled to a master-slave communication link. Most master-slave communication links are not addressable other than providing limited low-level hardware-based addressing, and peer-to-peer and broadcast operations initiated by the personal computers are often not supported due to the necessity for all communications to be funneled through the host computer.
Significant numbers of master-slave computer system installations exist throughout the world, and thus, the inability to communicate internetworking data over the master-slave communication links thereof often significantly limits the functionality of such installations. Short of scrapping a master-slave computer system and starting from scratch, one manner of resolving this problem is to install an additional LAN and/or WAN in a facility and couple the personal computers in the master-slave computer system to the additional network via additional hardware. However, installing an additional network can be a significant expense, principally due to hardware costs as well as the cost of installing additional wiring throughout a facility.
Given that the infrastructure for master-slave communication links is already in place for many existing master-slave computer systems, it would be much more cost effective to be able to communicate internetworking data over such links. Prior attempts to communicate internetworking data, however, utilize a dedicated gateway system coupled between a host computer and a LAN. The gateway system encapsulates data within a packet formatted using the transmission protocol of the host computer, then the host computer further encapsulates the packet using the transmission protocol of the master-slave communication link.
For example, for a Twinax attachment interface, a gateway system has been used between a LAN and a host computer such as an AS/400 midrange computer to encapsulate TCP/IP datagrams or packets within an SNA header for communication by the AS/400 computer. Then, a workstation controller in the AS/400 computer further encapsulates the data within a TDLC header for transmission over the Twinax interface.
Encapsulating internetworking data using the transmission protocol of the host computer, and then the transmission protocol of the underlying master-slave communication link, requires a dedicated gateway system that encompasses specific hardware and software. Moreover, each workstation requires a special device driver, as well as a special network interface. As a result, prior attempts at encapsulation often still involve significant additional hardware and software expense.
Therefore, a significant need continues to exist for a manner of communicating internetworking data over an existing master-slave communication link that requires minimal modifications with minimal additional expenses.